Direct Sequence Code Division Multiple Access (DS-CDMA) allows signals to overlap in time and frequency so that CDMA signals from multiple users simultaneously operate in the same frequency band or spectrum. In principle, a source information digital data stream to be transmitted is impressed upon a much higher rate data stream generated by a pseudo-random noise (PN) code generator. This combination of a higher bit rate code signal with a lower bit rate information stream “spreads” the bandwidth of the information data stream. Each information data stream is allocated a unique PN or spreading code (or a PN code having a unique offset in time) to produce a signal that can be separately received at a receiving station. From a received composite signal of multiple, differently-coded signals, a PN coded information signal is isolated and demodulated by correlating the composite signal with a specific PN spreading code associated with that PN coded information signal. This inverse, de-spreading operation “compresses” the received signal to permit recovery of the original data and at the same time suppress interference from other users.
Wideband CDMA systems contain one or several radio frequency carriers. Each radio frequency carrier contains a number of spreading codes which may be allocated to provide different data rates to satisfy different mobile user requirements. Some of those spreading codes are used for traffic channels and some are used for common control channels such as random access channels, paging channels, broadcast channels, etc. In order to provide flexibility in how bandwidth and other radio resources are allocated in wideband CDMA systems, a “logical” cell is defined. Such a logical cell may be allocated one or more radio frequency carrier(s) thereby permitting resources associated with different carriers belonging to the same cell to be allocated, for example, to a single mobile station (MS or UE) such as a cell phone requiring a high bit rate connection. The additional carrier(s) effectively provide more traffic channels.
WCDMA systems often utilize transport channels which may be mapped to physical channels. The physical layer (layer 1) is the lowest layer in the OSI Reference Model and it supports functions required for the transmission of bit streams on the physical medium. Thus, the physical layer offers data transport services to higher layers. Access to these services is provided through the use of transport channels via the MAC sub-layer. Characteristics of a transport channel are defined by its transport format (or format set), specifying the physical layer processing to be applied to the transport channel in question, such as convolutional channel coding and interleaving, and any service-specific rate matching as may be needed. Thus, transport channels may represent services offered by Layer 1 to the higher layers.
Exemplary transport channels include (i) common transport channels such as BCH (broadcast channel, often used as a downlink (DL) transport channel to broadcast system and/or cell specific information), FACH (forward access channel), PCH (paging channel), RACH (random access channel), CPCH (common packet channel), and DSCH (downlink shared channel), and (ii) dedicated channels (DCH) which may be used on the uplink or downlink. The FACH transport channel is typically known as a downlink channel, and transmitted over an entire cell or over only part of a cell using a beam-forming antenna. The PCH transport channel is typically known as a downlink (DL) channel transmitted over a cell, and is associated with the transmission of physical layer generated paging indicators (e.g., to support efficient sleep-mode procedures).
It is known that on the DL the PCH and FACH transport channels may be combined on the same physical channel such as on the SCCPCH (Secondary Common Control Physical Channel). This may be achieved in the context of a cellular telecommunications network using a COMMON TRANSPORT CHANNEL SETUP REQUEST message sent from an RNC to a BS. The BS receives this message, and in response thereto configures itself so as to support its activation of the SCCPCH. Once activated, the SCCPCH exists on the interface between the BS and mobile stations in the cell(s) of the BS.
Unfortunately, the COMMON TRANSPORT CHANNEL SETUP REQUEST message may not include any information indicative of whether any other transport channel(s) (e.g., RACH) is/are using the same physical channel identified in the COMMON TRANSPORT CHANNEL SETUP REQUEST message. If another transport channel(s) is/are already using the same physical channel, then the requested set-up of the SCCPCH becomes more difficult. Additionally, problems can also arise from inconsistent channel assignment messages received by a BS from an RNC.
Accordingly, it will be apparent to those skilled in the art that there exists a need in the art for a system and/or method for determining whether or not a physical channel identified in a transport channel set-up request message is already being used by another transport channel. There also exists a need in the art for a system and/or method for checking the consistency of messages received by a BS from an RNC or other node(s) (e.g., to reduce the likelihood of inconsistent channel assignments for physical channels).
According to an exemplary embodiment of this invention, a base station (BS) in a cellular telecommunications network utilizes parameter(s) included in a received transport channel setup message (e.g., in a received COMMON TRANSPORT CHANNEL SETUP REQUEST message) in order to determine whether or not the physical channel identified in the setup message is already being used by another transport channel(s). Parameters included in the received setup message which may be utilized by the BS in making such a determination include, for example, cell ID, cell carrier ID, downlink scrambling code ID, downlink channelization code number or ID, and the like. The BS may use this determined information to monitor the consistency of physical channel setup messages received from a node such as an RNC (e.g., to make sure that the same channel identity is not set up several times and/or to reduce the likelihood of inconsistent channel assignments for physical channels). Optionally, the BS may also use this determined information (e.g., if it is determined that the same physical channel is already being used by another transport channel) to either (i) more efficiently configure the hardware (e.g., hardware on Tx/Rx board(s) of the BS), or (ii) deny or reject the requested setup.